Recent research indicates that lithium carbonate at therapeutic levels may be nephrotoxic. Renal lysosomal enzymes are elevated in other renal disorders, prior to detectable light microscopic or physiological changes. This study would examine patients on lithium for evidence of elevated renal lysosomal enzymes. If elevations are demonstrated, this would contribute further evidence for lithium nephrotoxicity. Further, it could provide a laboratory test to single out patients susceptible to subsequent renal damage, at a time when standard renal function tests may be normal.